1. Field of the Invention
This invention relates to an improved method of securing head suspension members to actuator arms for use in disk drives, and particularly relates to a method of securing the head suspension members to very thin shelf segments of actuator arms for the purposes of decreasing the internal spacing of storage disks in a conventional disk drive envelope and minimizing actuator arm shelf cracking during production.
2. Related Art
In a disk drive assembly the magnetic heads of the drive are secured to the distal ends of head suspension members. The proximal ends of these head suspension members are attached to an actuator having multiple arms with protruding shelf segments. The actuator is in turn connected to a servo or stepping motor. The magnetic heads of the drive are moved to selected tracks on the disks by means of the servo or stepping motor via the actuator, its arms and the connected head suspension members.
There are various methods of attaching head suspension members to an actuator arm. Such methods include glue, screws, clamps, and staking.
In one known staking method two head suspension members are attached to a shelf segment of an actuator arm by means of two staking members having short tubular stems each of which are aligned through holes in the head suspension members and into a through hole on opposing sides of the protruding shelf segment of the actuator arm. The stems of the staking members are thereafter forcibly expanded within the structural material of the shelf segment of the actuator arm by driving a ball bearing through the stem tubes.
This particular method, although effective, has several limitations. One limitation of this method is the requirement of using two separate staking procedures to attach two head suspension members. The individual staking members, being positioned on opposing sides of the arm shelf segment, have to be staked to the actuator arm in separate procedures (i.e. one from each side).
A further limitation of expanding the tubular stem portion of the staking members within the structural material of the shelf segment lies in the configuration of the acutator arm and its shelf segment. To allow expansion of two staking members within the structural material of the shelf segment there must be a significant thickness of the actuator arm and the shelf segment. The thickness of the shelf segment necessary to this method prevents an ideal back to back mounting of the head suspension members and thus prevents a decreased internal spacing of the disks which rotate in between the multiple arms of the actuator. Ideally the space between the disks should only be limited by the height of the magnetic heads and the thickness of the head suspension members.
The most significant limitation in expanding the stem of the staking members within the structural material of the shelf segment is the possibility of cracking the shelf segment during the staking procedure. Cracking of the shelf often occurs despite the given thickness of the actuator arm and shelf segment. The nature of the assembly employed in this method channels the force of the staking procedure directly into the material of the shelf segment. If there is even a slight structural defect in the material of the actuator arm or shelf segment or if the staking procedure is not performed correctly the shelf segment of the actuator arm will crack. Cracking of the shelf segment results in defective assemblies and is a costly problem in mass manufacturing the actuator arm assemblies. The staking procedure is one of the last assembly procedures to take place in the manufacturing process. If the shelf segment cracks during the staking procedure the entire semi-complete multiple arm actuator assembly must be discarded at a significant cost.
In response to these limitations another method of staking was developed in which only one staking member was employed. In this method two head suspension members are first attached to opposing sides of the flange of the staking member and then the staking member is subsequently secured to the actuator arm shelf in a single staking procedure. In using only one staking member the thickness of the actuator arm and shelf segment is decreased because the shelf segment only has to withstand the force of one staking procedure. Using this method simplifies manufacturing procedures and decreases disk spacing to some extent but it still has significant limitations.
The single staking member procedure allows a small decrease in the spacing of disks, but the spacing of the disks is still limited by the thickness of the shelf segment and the resulting space between the mountings of the head suspension members (i.e. the thickness of the flange of the staking member. Also the force exerted by the staking procedure is still channeled directly into the structural material of the shelf segment. Cracking within the structural material of the shelf segment still occurs due to structural limitations. As a result, a significant percentage of the actuator arm assemblies still have to be discarded.
The problem related to the cracking of the actuator arm becomes more severe with an anticipated change in structural materials to ceramics. The metallic materials presently used expand and contract slightly when exposed to changes in temperature due to a metallic material's inherent coefficient of thermal expansion. These expansions and contractions hinder the accurate placement of the magnetic heads on the disks.
Because ceramic materials have no coefficient of thermal expansion there is an anticipated change in actuator arm materials to ceramics. This change will increase the accuracy of head placement by eliminating thermal expansions and contractions. However, this change creates problems in attaching head suspension members to ceramic actuator arms by any type of staking method. Expanding a staking member within an actuator arm formed from a ceramic material is impossible without shattering the arm and shelf segment. The cracking problem described is a major hindrance in the development of technology related to ceramic actuator arms.
Accordingly a purpose of the present invention is to overcome the disadvantages of the prior art by providing an alternative assembly and method for securing head suspensions to very thin shelf segments of metallic and ceramic actuator arms.